1. Field of the Invention
The present invention relates to telecommunications and more particularly to an auxiliary interface device for use in a residential telephone subscriber line circuit to place a temporary hold on a subscriber's telephone line.
2. Description of the Prior Art
At the present time it is common for many residential telephone subscribers to have one or more extension telephones connected to what is called a single-part telephone line. During a typical call it is common for a subscriber/user to either interrupt the conversation for a short time period or to change from one phone to another at a different location. When changing phones with a call in progress, the first telephone has to be left off-hook while the user transfers to a second location where the second phonse is located, otherwise the phone company equipment will sense an on-hook condition and will accordingly disconnect the two parties. The first phone then remains off-hook during the remaining part of the conversation unless the user wishes to return to the first location to replace the phone on the hook switch. Although this is an obvious bother, if it is not done the user often forgets at the end of the conversation that the first phone was left off-hook making it impossible for an incoming call to get through to the subscriber even though the line is not otherwise being used. Neither situation is highly desirable either for the subscriber or the telephone company providing the service.
Many of the recent model phones are equipped with a "HOLD" button or key which, when operated, permits the subscriber to hang up the handset of the telephone instrument without causing the central office equipment to disconnect the call. The basic purpose of a hold circuit is to switch an artificial load across the line so that when the hook switch goes open, the artificial load will dissipate enough line current to keep the line seized in the central office. Functionally a hold button allows a user to momentarily interrupt a call and replace the handset on the hook switch without terminating the call. Then the user can return to the same phone to remove the hold and complete the conversation. If the user completes the call on a different phone without releasing the hold on the first phone, it is often necessary, depending on the phone model, to return to the first phone to remove the hold to unseize the line. Obviously the inclusion of a hold-key function in the telephone instrument is not a complete solution to the particular problem posed. Nor is the inclusion of a hold key with a timed release a complete solution to the particular problem, since the user only has a short interval in which to pick up a second phone on the same line before the line disconnects. Too long of a delay keeps the line seized (loaded) during the remaining period of the call and potentially seized even after the user has finished the call.
Some current model telephones have "hold" buttons that will allow the hold to be released by picking up an extension phone instrument. However, a hold can only be activated in one direction (by the phone with the hold key) unless of course both phones are equipped with a hold function key.
This invention is directed to a very simple and inexpensive device which overcomes the above problems.
A general object of the invention is the provision of a telephone hold circuit which can be added to existing telephones without extensive rewiring changes or mechanical modification of the phone instruments, and which will allow a hold condition to be placed or removed from whichever phone is used.
Another object of this invention is the provision of an interface device to interface between a telephone subscriber's line and two or more telephone instruments to permit the subscriber to place or remove a hold condition from whichever phone is used, i.e., a two-way hold function.